1. Field of the Invention
This invention relates to an engraver, and more particularly, it relates to a cylinder support and method for supporting a cylinder to be engraved in an engraver.
2. Description of Related Art
The basic principle of electro-mechanical engraving of a gravure cylinder involves rotating a plated cylinder while actuating an electrically driven tool which cuts or engraves cells or lines into the surface of the plated cylinder. The engraved cylinder is normally used in a web-type gravure printing press for printing paper, plastic or metallic film material. In addition to printing newspapers and magazines, the engraved cylinders may also be used for direct or indirect printing of cloth, applying glue, printing of packaging materials for products, and printing of woodgrain patterns for making wall panelling, floor coverings and other surface coverings.
In the gravure printing process, the engraved cylinder is flooded with ink, and a doctor blade wipes off excess ink from the surface so that only the engraved cells contain ink which is transferred to the material being printed. To obtain a high quality print, it is necessary that the cells be very accurately placed or located on the cylinder surface, usually within 1 or 2 microns of a desired predetermined location. The depth of the engraved cells must also be accurately controlled since the depth determines the amount of ink transferred which, for example, determines the shade of gray in a black/white print. In a color print, the amount of ink transferred to the paper or materials is even more critical since multiple colors are typically mixed to produce various hues. A slight variation in the desired amount of ink affects not only the darkness of the color but, more importantly, the production of the desired color hues.
In engraving systems of the past, a cylinder was manually guided or hoisted to an engraving area of the engraver, whereupon it was secured between a stationary headstock and a slidable tailstock. The tailstock forcibly engaged one end of the cylinder and forced the other end of the cylinder into engagement with the headstock. For a shafted cylinder, the ends of the cylinder would be gripped by chucks or other clamping devices located in the headstock and tailstock.
Another problem with engravers of the past is that the cylinders had to be manually loaded into the engraver. Because of the weight and size of the cylinders, it was very time-consuming to properly position and manually align the cylinders in the engraver. In addition, it was often necessary that the operator manually adjust the tailstock before the engraver could accommodate cylinders of varying lengths. Still another problem is that in the engravers of the past, the operator had to manually adjust the engraving head to accommodate cylinders of different diameters.
This alignment problem is particularly acute where shafted cylinders are supported by chucks for engraving. Collet chucks used to support such shafted cylinders may have a clearance of as little as 0.005 inch (approximately 0.0127 cm). It is very difficult to manually align shafts within such a tight clearance, even without the added difficulty of the weight and size of the cylinder.
What is needed, therefore, is a method and apparatus for facilitating loading a cylinder in an engraver and for handling the cylinder so that it can be easily centered and aligned between the headstock and tailstock of the engraver.